What is the easiest way to find and replace text in 20 text files in a directory?
Notepad++ can do it easily...
Search menu → Find in Files... menu item.
In Notepad++ 7.9.2
Go to
File → Open Containing Folder → Folder as Workspcae
Right click on your folder and select Find in Files...
In Find in Files dialog, click on tab Find in Files and fill your keyword in Find what then fill the replacement in Replace with and click on Find All button to find all occurrences keyword in all files, or Replace in Files button, to replace all occurrences of keyword with its replacement.
GrepWin would do this among others, and it is a Explorer plugin.
However there is quite a big array of different applications available that can do this.
This SO thread on the topic also suggest WinGrep as an option.
If you are familiar with Visual Studio, you can do that without creating a project. Do (something like): Edit>Find/Replace>Find in Files. There you can specify a folder.
I've done this many times. I'd say it's only overkill if you had to create a project (you don't) or if you didn't have VS installed and needed it only for this request.